We have recently found a strong circadian rhythmicity in insulin sensitivity in patients with NIDDM which was due primarily to rhythmic changes in HGP. The circadian changes in HGP, in turn, were associated with corresponding rhythmic changes in plasma FFA and plasma cortisol levels. Both plasma FFA and cortisol levels correlated negatively with insulin sensitivity (r=-0.72 and -0.64 respectively). The purpose of this study will be to determine whether the changes in plasma FFA are the cause for the circadian rhythmicity of HGP.